Honeycomb filter

ABSTRACT

A honeycomb filter of the present invention is a honeycomb filter  10  including a number of through-holes  12  surrounded by partition walls and extending through an axial direction, in which the partition walls have filterability, predetermined through-holes  12  are plugged at one end portion, and the remaining through-holes  12  are plugged at the other end portion to trap particulate matter contained in a dust-containing fluid. The honeycomb filter is characterized in that a heat capacity of a central part  11  is set to be larger than that of a peripheral part  13  in a section of the honeycomb filter  10  perpendicular to the axial direction. There is provided a honeycomb filter in which a crack is not generated by thermal stress during use, especially at a regeneration time and which is superior in durability.

TECHNICAL FIELD

The present invention relates to a honeycomb filter for trappingparticulate matter contained in dust-containing fluid such as exhaustgas emitted from a diesel engine.

BACKGROUND ART

A honeycomb structure has heretofore been used as a filter for trappingparticulate matter contained in a dust-containing fluid such as exhaustgas emitted from a diesel engine.

In the honeycomb structure used for such a purpose, the rapidtemperature change of exhaust gas and the local heating easily makesnon-uniform the temperature distribution inside the honeycomb structure,which makes problems such as crack generation in the honeycomb structureand the like. When the honeycomb structure is used particularly as afilter for trapping particulate matter in exhaust gas emitted from adiesel engine, it is necessary to burn the fine carbon particlesdeposited on the filter to remove the particles and regenerate thefilter. In that case, high temperatures are inevitably generated locallyin the filter. As a result, a large thermal stress and cracks tend to begenerated. Here, the thermal stress is generated because thermalexpansion/deformation of each part of the honeycomb structure differs bythe non-uniformity of the temperature distribution, in which thetemperature of a central part becomes higher than that of a peripheralpart, and the parts are mutually restrained and are not freelydeformable.

The above-described problem is remarkable especially in a honeycombfilter of SiC. That is, through the honeycomb filter of SiC is superiorin heat resistance, the filter disadvantageously has a coefficient ofthermal expansion which is higher than that of a conventionally-knowncordierite honeycomb filter, and is inferior to the conventional filterin a thermal shock resistance.

To avoid this disadvantage, there has been known a measure of dividingstructural parts into smaller segments to reduce the stress, and aproposal for applying this measure to the honeycomb structure fortrapping particulates in the exhaust gas has been already described, forexample, in JP-A-6-241017, JP-A-8-28246, JP-A-7-54643, and JP-A-8-28248.

However, since a thermal conductivity in a radial direction drops in thestructure described in the above proposals, the thermal shock resistanceis not much enhanced. Therefore, a stress reducing effect on the segmentsurface is insufficient, and the problem of crack generation cannot becompletely solved.

The present invention has been developed in consideration of theconventional problems and aims to provide a honeycomb filter in which acrack is not generated by thermal stress generated at a use time,especially at a regeneration time and which is superior in durability.

DISCLOSURE OF THE PRESENT INVENTION

As the first aspect of the present invention, there is provided ahoneycomb filter for trapping particulate matter contained indust-containing fluid, the filter comprising a number of through-holessurrounded by partition walls and extending in an axial direction, thepartition walls having filterability, predetermined through-holes beingplugged at one end, remaining through-holes being plugged at the otherend, wherein in a section of the honeycomb filter perpendicular to theaxial direction, a heat capacity in a central part of the honeycombfilter is higher than that in a peripheral part of the honeycomb filter.

As the second aspect of the present invention, there is provided ahoneycomb filter for trapping particulate matter contained indust-containing fluid, the filter comprising a number of through-holessurrounded by partition walls and extending in an axial direction, thepartition walls having filterability, predetermined through-holes beingplugged at one end, remaining through-holes being plugged at the otherend, wherein the honeycomb filter comprises an assembly of a pluralityof honeycomb segments, and in a section of each honeycomb segmentperpendicular to the axial direction, a heat capacity of a central partof the honeycomb filter is higher than that of a peripheral part of thehoneycomb filter.

In the present invention, preferable embodiments in which a heatcapacity of the central part of the honeycomb filter or the central partof each honeycomb segment is set to be higher than that of a peripheralpart are as follows:

(1) a non-plugged through-hole end portion is plugged in the centralpart of the honeycomb filter or in the central part of the honeycombsegment in the end face of the honeycomb filter in the axial direction;

(2) a thickness of a partition wall in the central part of the honeycombfilter or in the central part of the honeycomb segment in the sectionperpendicular to the axial direction is set to be larger than that ofthe partition wall in the peripheral part;

(3) the thickness of the partition wall in the central part of thehoneycomb segment is set to be 1.02 to 1.5 times that of the partitionwall in the peripheral part of the honeycomb segment in the section ofthe honeycomb filter perpendicular to the axial direction;

(4) the thickness of the partition wall is gradually reduced toward theperipheral part from the central part with respect to some or all of thepartition walls of the honeycomb segment in the section of the honeycombfilter perpendicular to the axial direction;

(5) a cell density in the central part of the honeycomb filter or in thecentral part of the honeycomb segment in the section perpendicular tothe axial direction is set to be larger than that in the peripheral partof the filter or the segment;

(6) a bonding material of the honeycomb segment positioned in thecentral part of the honeycomb filter in the section perpendicular to theaxial direction is set to be thicker than that of the honeycomb segmentpositioned in the peripheral part;

(7) a thermal conductivity of the honeycomb segment positioned in thecentral part of the honeycomb filter in the section perpendicular to theaxial direction is set to be higher than that of the honeycomb segmentpositioned in the peripheral part; and

(8) the plugging is performed in the honeycomb filter such that aplugging depth is large in the central part of the honeycomb filter orin the central part of the honeycomb segment, and small in theperipheral part of the filter or the segment, so that the heat capacityof the central part of the honeycomb filter is larger than that of theperipheral part.

As an area of the honeycomb segment positioned in the central part, asectional area of the central part of the honeycomb segment is set topreferably 40 to 90% of that of the whole honeycomb segment in thesection of the honeycomb filter perpendicular to the axial direction.

Moreover, a material for the honeycomb filter preferably contains oneselected from the group consisting of SiC, Si₃N₄, alumina, mullite,aluminum titanate, zirconium phosphate, and lithium aluminum silicate asa main crystal phase, and especially SiC is preferable because its heatresistance is superior. The sectional shape of the through-holes of thehoneycomb filter is preferably any of a triangle, a tetragon, a hexagonand a corrugated shape from the standpoint of production.

Furthermore, the honeycomb segment preferably carries a catalyst becausethe filter not only traps the particulate matter but also has a functionof purifying the exhaust gas or the like is provided, and the catalystfurther preferably contains at least one of Pt, Pd, Rh, K, Li, and Na.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing an end face of an embodiment of ahoneycomb filter of the present invention.

FIG. 2 is an explanatory view showing an end face of another embodimentof a honeycomb filter of the present invention.

FIG. 3 is an explanatory view showing an end face of another embodimentof a honeycomb filter of the present invention.

FIG. 4 is an explanatory sectional view showing another embodiment of ahoneycomb filter of the present invention.

FIG. 5 is an explanatory sectional view showing another embodiment of ahoneycomb filter of the present invention.

FIG. 6 is an explanatory partially sectional view showing anotherembodiment of a honeycomb filter of the present invention.

FIG. 7 is an explanatory sectional view showing another embodiment of ahoneycomb filter of the present invention.

FIG. 8 are explanatory sectional views showing other embodiments of ahoneycomb filter of the present invention, FIG. 8( a) shows a case whereonly a central part of a honeycomb segment has a thick partition wall,and FIG. 8( b) shows a case where the partition wall of the honeycombsegment is formed in a thick cross shape;

FIG. 9 is an explanatory sectional view showing another embodiment of ahoneycomb filter of the present invention.

FIG. 10 is a graph showing temperature distribution on a honeycombfilter in regeneration.

BEST MODE FOR CARRYING OUT THE INVENTION

In a honeycomb filter of the present invention, a section of the filterperpendicular to the axial direction is formed in such a manner that aheat capacity of a central part of the honeycomb filter is higher thanthat of a peripheral part or that a heat capacity of a central part of ahoneycomb segment is higher than that of a peripheral part of thehoneycomb segment. Accordingly, during use, especially at a regenerationtime, a temperature rise in the central part whose temperature tends torise more easily than in the peripheral part is suppressed, and atemperature difference between the central part and the peripheral partcan be reduced. Therefore, cracks can be inhibited from being generatedeven by thermal stress caused in the honeycomb filter, and the filter isremarkably superior in durability.

The present invention will be described hereinafter in more detail basedon embodiments. However, the present invention is not limited to theseembodiments.

The present invention is a honeycomb filter for trapping particulatematter contained in a dust-containing fluid. The filter has a number ofthrough-holes surrounded by partition walls and extending in an axialdirection, the partition walls of the through-holes have filterability,predetermined through-holes are plugged at one end portion, and theremaining through-holes are plugged at the other end portion.

As a concrete method for setting the heat capacity of a central part ofthe honeycomb filter of the present invention constituted as describedabove or a central part of a honeycomb segment to be higher than that ofa peripheral part, there are the following various embodiments. That is:

(1) a non-plugged through-hole end portion is plugged in the centralpart of the honeycomb filter or in the central part of the honeycombsegment in the end face of the honeycomb filter in the axial direction;

(2) a thickness of a partition wall in the central part of the honeycombfilter or in the central part of the honeycomb segment in the sectionperpendicular to the axial direction is set to be larger than that ofthe partition wall in the peripheral part;

(3) the thickness of the partition wall in the central part of thehoneycomb segment is set to be 1.02 to 1.5 times that of the partitionwall in the peripheral part of the honeycomb segment in the section ofthe honeycomb filter perpendicular to the axial direction;

(4) the thickness of the partition wall is gradually reduced toward theperipheral part from the central part with respect to some or all of thepartition walls of the honeycomb segment in the section of the honeycombfilter perpendicular to the axial direction;

(5) a cell density in the central part of the honeycomb filter or in thecentral part of the honeycomb segment in the section perpendicular tothe axial direction is set to be larger than that in the peripheral partof the filter or the segment;

(6) a bonding material of the honeycomb segment positioned in thecentral part of the honeycomb filter in the section perpendicular to theaxial direction is set to be thicker than that of the honeycomb segmentpositioned in the peripheral part;

(7) a thermal conductivity of the honeycomb segment positioned in thecentral part of the honeycomb filter in the section perpendicular to theaxial direction is set to be higher than that of the honeycomb segmentpositioned in the peripheral part; and

(8) the plugging is performed in the honeycomb filter such that aplugging depth is large in the central part of the honeycomb filter orin the central part of the honeycomb segment, and small in theperipheral part of the filter or the segment, so that the heat capacityof the central part of the honeycomb filter is larger than that of theperipheral part.

The above-described embodiments will be concretely describedhereinafter.

First, an embodiment of setting the heat capacity of the central part tobe larger than that of the peripheral part in the honeycomb filter ofthe present invention can be largely classified into two. First, thehoneycomb filter is constituted by a single body. Secondly, thehoneycomb filter comprises a plurality of honeycomb segments, and therespective honeycomb segments are bonded via a bonding material toconstitute the honeycomb filter.

When the honeycomb filter is constituted by a single body, as the firstembodiment, the end portions of the through-holes which are not usuallyplugged are plugged in the central part of the end face of the honeycombfilter in the axial direction.

As shown in FIG. 1, in a central part 11 in the end face of a honeycombfilter 10 in the axial direction, the end portions of through-holes 12are usually alternately plugged. However, in this case, the end portionsof the through-holes 12 which are not usually plugged are furtherplugged. Accordingly, the heat capacity of the central part 11 can beset to be larger than that of a peripheral part 13.

Moreover, the object to set the heat capacity of the central part 11 tobe larger than that of the peripheral part 13 can be achieved also whena plugging depth is increased in the central part 11 among the pluggedend portions of the through-holes 12.

In the above-described constitution, since an amount of soot depositedin the central part 11 becomes smaller than that in the peripheral part,there is a merit that a temperature rise at a filter regeneration time(soot burning time) can be suppressed.

Here, defining that a certain region extending inwardly from an outerperipheral contour of the honeycomb filter (or the honeycomb segment) isthe outer peripheral part, and a remaining region (further inner region)is the central part, an area range of the central part is set to 20 to90% of that of a sectional area of the honeycomb filter (or thehoneycomb segment). Examples of the region of the central part include aregion surrounded by a shape analogous to a sectional shape of an outerperipheral surface centering on a center point on the section of thehoneycomb filter (or the honeycomb segment), and a region surrounded bya circle centering on the center point. The area range of the centralpart is preferably 40 to 90%, further preferably 50 to 90% of thesectional area of the honeycomb filter (or the honeycomb segment).

As the second embodiment, for example, the thickness of the partitionwall in the central part of the section of the honeycomb filterperpendicular to the axial direction is set to be larger than that ofthe partition wall in the peripheral part.

As shown in FIG. 2, in the section of the honeycomb filter 10perpendicular to the axial direction, the thickness of a partition wall14 a in the central part 11 is formed to be larger than that of apartition wall 14 b in the peripheral part 13. Accordingly, the heatcapacity of the central part 11 can be set to be higher than that of theperipheral part 13. Furthermore, in this constitution, resistance at atime when the exhaust gas passes through the partition wall in thecentral part of the honeycomb filter increases as compared with that inthe peripheral part. Therefore, the amount of exhaust gas flowingthrough the central part of the honeycomb filter drops, and an amount ofdeposited particulate matter is also decreased. Therefore, the amount ofheat generated in the central part of the honeycomb filter at theregeneration time relatively drops as compared with the outer peripheralpart, temperature distribution of the honeycomb filter in a sectionaldirection is uniformalized, and a problem that the honeycomb filter iscracked at the regeneration time is solved.

In addition, as the third embodiment, as shown in FIG. 3, also when acell density of the central part 11 is set to be larger than that of theperipheral part 13 in the section of the honeycomb filter 10perpendicular to the axial direction, the heat capacity of the centralpart 11 can be set to be larger than that of the peripheral part 13 inthe same manner as described above.

Next, the case where the honeycomb filter comprises a plurality ofhoneycomb segments and the respective honeycomb segments are bonded bythe bonding material to constitute the honeycomb filter will bedescribed.

In this manner, also when the plurality of honeycomb segments are bondedby the bonding material to constitute the honeycomb filter, the heatcapacity of the filter central part can be set to be larger than that ofthe peripheral part by various embodiments as described below.Similarly, the heat capacity of the central part of each honeycombsegment can be set to be larger than that of the peripheral part.

First, as shown in FIG. 4, honeycomb segments 15 are bonded to oneanother by a bonding material 20 only in the central part of thehoneycomb filter 10.

Moreover, as shown in FIG. 5, the thickness of the partition wall of ahoneycomb segment 15 a positioned in the central part 11 is set to belarger than that of the partition wall of a honeycomb segment 15 bpositioned in the peripheral part 13 in section of the honeycomb filter10 perpendicular to the axial direction. In this constitution, in thesame manner as in the case where the partition wall in the central partof the honeycomb filter is thickened, the amount of depositedparticulate matter can be decreased. Therefore, the amount of heatgenerated in the central part of the honeycomb segment at theregeneration time relatively drops as compared with the outer peripheralpart, and a problem that the honeycomb segment is cracked at theregeneration time is solved.

Furthermore, as shown in FIG. 6, in the section of the honeycomb filterperpendicular to the axial direction, a bonding material 20 a for use inbonding the honeycomb segment 15 a positioned in the central part 11 isformed to be thicker than a bonding material 20 b for use in bonding thehoneycomb segment 15 b positioned in the peripheral part 13.

Additionally, in the section of the honeycomb filter perpendicular tothe axial direction, the thermal conductivity of the honeycomb segmentpositioned in the central part is set to be larger than that of thehoneycomb segment positioned in the peripheral part in a preferableembodiment.

Furthermore, in both the honeycomb filter integrally constituted by asingle body and the honeycomb filter comprising a plurality of honeycombsegments, as shown in FIG. 7, plugging portions 16 are formed such thatthe plugging depth is large in the central part and small in theperipheral part. Accordingly, the heat capacity of the central part ofthe honeycomb filter 10 becomes larger than that of the peripheral part.This may be said to be a preferable embodiment. In each honeycombsegment, the heat capacity of the central part is set to be larger thanthat of the peripheral part as another preferable embodiment.

Additionally, when the honeycomb filter comprises a plurality ofhoneycomb segments, as shown in FIG. 8( a), partition walls 14 c in thecentral part of the honeycomb segment 15 is formed to be thicker thanpartition walls 14 d in the peripheral part as another preferableembodiment. As shown in FIG. 8( b), partition walls 14 e are formed tobe thick in a cross form in each honeycomb segment 15 as still anotherpreferable embodiment.

The thickness of the partition wall in the central part of the honeycombsegment is preferably 1.02 to 1.5 times that of the partition wall inthe peripheral part of the honeycomb segment. When the wall is thick 1.5times, a air flow resistance of the whole honeycomb filter tends toincrease.

Moreover, as shown in FIG. 9, in some or all of partition walls 17 inthe section of the honeycomb segment 15, the thickness may be graduallyincreased toward the inside from a position of a contact 30 of an outerperipheral wall 18. Furthermore, the thickness of the partition wall 17partitioning each through-hole 12 may be successively increased towardthe inside from the outside. Here, “being gradually increased” meansthat an average thickness of the partition wall 17 which partitions thethrough-hole 12 positioned in a peripheral side is increased. Forexample, the thickness may be continuously changed as shown in FIG. 9,or the thickness may also be changed for each partition wall 17 whichpartitions one through-hole 12.

The thickness of the partition wall of the honeycomb segment is in arange of preferably 50 to 2,000 μm. When the thickness of the partitionwall is less than 50 μm, strength of the honeycomb segment becomesinsufficient. When the thickness exceeds 2000 μm, effective geometricsurface area (GSA) of the honeycomb segment drops, and a pressure lossincreases when the gas flows.

In the present invention, the sectional area of the central part of thehoneycomb segment is preferably 40 to 90%, further preferably 50 to 90%of that of the whole honeycomb segment in the section of the honeycombfilter perpendicular to the axial direction.

A sectional shape of the section of the honeycomb filter perpendicularto the through-hole in the present invention may be various shapes suchas a circle, an ellipse, and a race track shape.

Moreover, in the honeycomb filter of the present invention, as describedabove, an embodiment in which two or more honeycomb segments arecombined/constituted may be employed. A material for the filterpreferably contains one selected from the group consisting of SiC,Si₃N₄, alumina, mullite, aluminum titanate, zirconium phosphate, andlithium aluminum silicate as a main crystal phase from standpoints ofstrength, thermal resistance or the like, and SiC having a high thermalconductivity is especially preferable in that heat is easily discharged.

The cell density of cells formed by the partition walls is preferably 6to 2000 cells/square inch (0.9 to 311 cells/cm²), further preferably 50to 400 cells/square inch (7.8 to 62 cells/cm²). When the cell density isless than 6 cells/square inch (0.9 cells/cm²), the strength andeffective geometric surface area (GSA) of the honeycomb segment becomeinsufficient. When the density exceeds 2000 cells/square inch (311cells/cm²), the pressure loss increases when the gas flows.

There is no particular restriction as to the sectional shape ofthrough-holes (cell shape). However, the sectional shape is preferablyany of a triangle, a tetragon, a hexagon and a corrugated shape from thestandpoint of production.

Moreover, as the bonding material for bonding the honeycomb segments andas the plugging material, a ceramic fiber, ceramic powder, or cementhaving heat resistance is preferably used alone, or they are mixed foruse. Furthermore, if necessary, an organic binder, an inorganic binderor the like may also be mixed and used.

When a dust-containing fluid is passed from one end face of thehoneycomb filter of the present invention, the dust-containing fluidflows into the honeycomb filter via the through-holes whose end portionson one end face side are not plugged. The fluid passes through porouspartition walls having filterability, and enters the other through-holesthat are not plugged on the side of the other end face of the honeycombfilter. The particulate matter in the dust-containing fluid is trappedby the partition walls when the fluid passes through the partitionwalls, and the purified fluid from which the particulate matter has beenremoved is discharged from the other end face of the honeycomb filter.

It is to be noted that when the trapped particulate matter is depositedon the partition wall, clogging occurs, and the function of the filteris deteriorated. Therefore, by periodically heated the honeycomb filterby a heating means such as a heater, the particulate matter isburnt/removed, and the filter function is regenerated. To promote theburning of the particulate matter at the regeneration time, a metalhaving catalytic activity may be loaded on the honeycomb filter.

It is preferred that the honeycomb filter of the present invention isloaded with a catalyst, for example, a metal having a catalytic activitywhen the present honeycomb filter is intended to use as a catalystcarrier for purifying exhaust gas emitted from a heat engine such asinternal combustion engine or the like or from a burner such as boileror the like, or for reforming liquid fuel or gaseous fuel. As arepresentative metal having a catalytic activity, Pt, Pd, Rh, K, Li andNa are mentioned, and it is preferred to load at least one kind of theseon the honeycomb filter.

Next, methods of producing the honeycomb filter of the present inventionwill be described, but the method of producing the honeycomb filter ofthe present invention is not limited to these methods.

As a raw material powder for the honeycomb segment, the above-describedpreferable materials such as a silicon carbide powder are used. To thepowder, binders such as methyl cellulose and hydroxypropoxylmethylcellulose are added. Further, a surface-active agent and water areadded to prepare clay having plasticity. The clay is extruded to formhoneycomb segments as shown, for example, in FIGS. 4, 5, 8(a), 8(b), and9.

After drying the honeycomb segments, for example, with microwaves andhot air, the outer peripheral surface of the honeycomb segment is coatedwith the bonding material having the same composition as that of theclay, and the honeycomb segments are bonded, assembled, and dried. Theobtained assembled dry body is heated/degreased, for example, in anitrogen atmosphere, and subsequently heated in an inert atmosphere suchas Ar atmosphere so that the honeycomb filter of the present inventioncan be obtained.

In the present invention, as a method of bonding the honeycomb segments,in addition to the method of directly applying the outer peripheralsurface with the bonding material as described above, a plate formed bya bonding material in a predetermined thickness may be used, and ahoneycomb segment may be bonded to another honeycomb segment by theplate and the bonding material.

After producing the honeycomb filter in the above-described method, theend face of the honeycomb filter can be plugged with a raw materialsimilar to that of the honeycomb segment.

Catalyst may be loaded on the thus-produced honeycomb filter by a methodordinarily used by those skilled in the art, for example, bywash-coating a catalyst slurry on the honeycomb filter, and thenconducting drying and firing.

EXAMPLES

The present invention is described in more detail below by way ofExamples. However, the present invention is not restricted to theseExamples.

Examples 1 to 8, Comparative Examples 1 to 4

Regeneration limit was evaluated using a honeycomb filter havingmaterial characteristics such as a porosity of 45%, an average porediameter of 10 μm, and a thermal conductivity of 40 W/mK and comprisinga honeycomb structure of SiC having a diameter of 5.66 inches and alength of 6 inches and having a plugging depth of 3 mm. In theevaluation of the regeneration limit, a predetermined amount ofartificially produced soot was deposited on the honeycomb filter, and ahigh-temperature gas was introduced at 600° C., 2.3 Nm³/min toregenerate the filter (burn the soot). Thereafter, a limit soot amountin which any crack was not generated was set to a regeneration limit. Itis to be noted that a dimension of nine segments in Examples 4 to 7,Comparative Examples 2, 4 was basically 58 mm, and an outer peripheralsegment was worked in a predetermined outer dimension in accordance witha product outer shape.

The results are shown in Table 1.

Moreover, in the honeycomb filter described in Example 1, the amount ofdeposited soot was 10 g/L, and a high-temperature gas having an O₂concentration of 10% was introduced at 600° C., 0.7 Nm³/min toregenerate/burn the honeycomb filter. The results of measurement of atemperature distribution at the regeneration time in this case are shownin FIG. 10. In FIG. 10, r(m) denotes a length in a radial direction,X(m) denotes a length in an axial direction, lines shown in a graph areisothermal lines indicating a temperature distribution, and numericvalues indicate temperatures of the isothermal lines (unit:° C.).

TABLE 1 SiC material Example, Cell Comparative structure RegenerationExample mil/cpi Additional structure limit (g/L) Example 1 12/200Central part additional 18 plugged 100 cells Example 2 12/200 Wallthickness of central part 20 15 mil, radial direction 50% length regionExample 3 12/200 Central part 350 cpi, radial 18 direction 50% lengthregion Example 4 12/200 9 segments, bonding thickness 20 3 mm, segmentcentral part in cross form, 7 cells added in width, 15/200 structure,cell thickness increase Example 5 12/200 9 segments, central segments 2014/200, bonding thickness 3 mm Example 6 12/200 9 segments, centralsegment 18 peripheral bonding thickness 5 mm, another bonded portion 1mm Example 7 12/200 9 segments, central part 16 segment thermalconductivity 1.5 times, bonding thickness 1 mm Example 8 12/200 Centralpart plugging depth 30 mm, 18 peripheral part 3 mm, depth distributionproportional to distance from center Comparative 12/200 Plugging depth 3mm 12 Example 1 Comparative 12/200 9 segments, uniform bonding 10Example 2 thickness 1 mm Comparative 15/200 Plugging depth 3 mm 12Example 3 Comparative 14/200 9 segments, uniform bonding  8 Example 4thickness 3 mm

Examples 9 to 16, Comparative Examples 5 to 8

The regeneration limit was evaluated with respect to honeycomb filterswhich were the same as those of Examples 1 to 8 and Comparative Examples1 to 4 except for different cell structures. The results are shown inTable 2.

TABLE 2 SiC material - Example, Cell Comparative structure RegenerationExample mil/cpi Additional structure limit (g/L) Example 9 12/300Central part additional 20 plugged 150 cells Example 10 12/300 Wallthickness of central part 22 15 mil, radial direction 50% length regionExample 11 12/300 Central part 350 cpi, radial 16 direction 50% lengthregion Example 12 12/300 9 segments, bonding thickness 20 3 mm, segmentcentral part in cross shape, 7 cells in width, 15/200 structure, cellthickness increase Example 13 12/300 9 segments, central segment 1814/200, bonding thickness 3 mm Example 14 12/300 9 segments, centralsegment 16 peripheral bonding thickness 5 mm, other bonded portion 1 mmExample 15 12/300 9 segments, central part 18 segment thermalconductivity 1.5 times, bonding thickness 1 mm Example 16 12/300 Centralpart plugging depth 30 mm, 20 peripheral part 3 mm, depth distributionproportional to distance from center Comparative 12/300 Plugging depth 3mm 12 Example 5 Comparative 12/300 9 segments, uniform bonding 12Example 6 thickness 1 mm Comparative 15/300 Plugging depth 3 mm 10Example 7 Comparative 14/300 9 segments, uniform bonding 10 Example 8thickness 3 mm

Examples 17 to 18, Comparative Examples 10 to 11

The regeneration limit was evaluated with respect to honeycomb filterswhich were the same as those of Examples 1 to 8, Comparative Examples 1to 4 except that cordierite was used as the material, cell structureswith 12 mil/200 cpi, 12 mil/300 cpi were used, and the cell thickness ofthe honeycomb segment central part was increased to 15 mil. The resultsare shown in Table 3.

Examples 19 to 25, Comparative Examples 12 to 13

SiC was used as a material, 12 mil/200 cpi, 12 mil/300 cpi were used asa cell structure, the cell thickness was increased in a predeterminedarea portion in the central part of a honeycomb segment as shown in FIG.8( a), and regeneration limits of Examples 19 to 25 were evaluated. Theresults of the evaluation of a uniform thickness are shown inComparative Examples 12, 13.

TABLE 3 Cordierite & SiC material Example, Cell Regeneration Comparativestructure limit Example mil/cpi Additional structure (g/L) Example 1712/200 9 segments, uniform bonding 16 thickness 1 mm, segment centralpart 5 cell square 15/200 Example 18 12/300 9 segments, uniform bonding16 thickness 1 mm, segment central part 5 cell square 15/300 Comparative12/200 9 segments, uniform bonding  8 Example 10 thickness 1 mmComparative 12/300 9 segments, uniform bonding 10 Example 11 thickness 1mm Example 19 12/300 9 segments, uniform bonding 20 thickness 1 mm,central part wall thickness 2% increase, central part area 90% Example20 12/300 9 segments, uniform bonding 22 thickness 1 mm, central partwall thickness 5% increase, central part area 90% Example 21 12/300 9segments, uniform bonding 20 thickness 1 mm, central part wall thickness5% increase, central part area 80% Example 22 12/300 9 segments, uniformbonding 18 thickness 1 mm, central part wall thickness 50% increase,central part area 70% Example 23 12/300 9 segments, uniform bonding 18thickness 1 mm, central part wall thickness 2% increase, central partarea 70% Example 24 15/200 9 segments, uniform bonding 20 thickness 1mm, central part wall thickness 2% increase, central part area 90%Example 25 15/200 9 segments, uniform bonding 20 thickness 1 mm, centralpart wall thickness 5% increase, central part area 80% Comparative12/300 9 segments, uniform bonding 12 Example 12 thickness 1 mmComparative 15/200 9 segments, uniform bonding 12 Example 13 thickness 1mm

INDUSTRIAL APPLICABILITY

As described above, according to a honeycomb filter of the presentinvention, during use, especially at a regeneration time, a temperaturerise is suppressed in a central part of the honeycomb filter or acentral part of each honeycomb segment whose temperature tends to riseas compared with a peripheral part. A temperature difference between thecentral part and the peripheral part of honeycomb filter or between thecentral part and the peripheral part of each honeycomb segment isreduced, and a thermal stress generated in the honeycomb filter can bereduced. As a result, any crack can be inhibited from being generated inthe honeycomb filter, and the filter has a superior effect thatdurability is remarkably superior.

1. A honeycomb filter for trapping particulate matter contained indust-containing fluid, the filter comprising: a number of through-holessurrounded by partition walls and extending in an axial direction, thepartition walls having filterability, predetermined through-holes beingplugged at one end, remaining through-holes being plugged at the otherend, wherein in a section of the honeycomb filter perpendicular to theaxial direction, heat capacity in a central part of the honeycomb filteris higher than that in a peripheral part of the honeycomb filter,wherein in the section of the honeycomb filter perpendicular to theaxial direction, a thickness of the partition wall in the central partis set to be larger than that of the partition wall in the peripheralpart.
 2. The honeycomb filter according to claim 1, wherein in an endface of the honeycomb filter in the axial direction, a non-pluggedthrough-hole end portion is plugged in the central part of the honeycombfilter.
 3. The honeycomb filter according to claim 1, wherein in thesection of the honeycomb filter perpendicular to the axial direction, acell density in the central part is set to be larger than that in theperipheral part.
 4. The honeycomb filter according to claim 1, whereinthe plugging is performed in the honeycomb filter such that a pluggingdepth is large in the central part, and small in the peripheral part, sothat a heat capacity in the central part of the honeycomb filter is setto be larger than that in the peripheral part.
 5. A honeycomb filter fortrapping particulate matter contained in dust-containing fluid, thefilter comprising: a number of through-holes surrounded by partitionwalls and extending in an axial direction, the partitionwalls havingfilterability, predetermined through-holes being plugged at one end,remaining through-holes being plugged at the other end, wherein thehoneycomb filter comprises an assembly of a plurality of honeycombsegments, and in a section of each honeycomb segment perpendicular tothe axial direction, a heat capacity of a central part of the honeycombfilter is higher than that of a peripheral part of the honeycomb filter,and in a section of the honeycomb filter perpendicular to the axialdirection, a thickness of the partition wall of the honeycomb segmentpositioned in a central part of the honeycomb filter is set to be largerthan that of the partition wall of the honeycomb segment positioned in aperipheral part.
 6. The honeycomb filter according to claim 5, whereinthe honeycomb filter comprises a plurality of the honeycomb segmentsbonded by a bonding material.
 7. The honeycomb filter according to claim6, wherein the thickness of the partition wall in the central part ofthe honeycomb segment is set to 1.02 to 1.5 times that of the partitionwall in the peripheral part of the honeycomb segment.
 8. The honeycombfilter according to claim 5, wherein in the section of the honeycombfilter perpendicular to the axial direction, a sectional area of thecentral part of the honeycomb segment is set to 90% or less of that ofthe whole honeycomb segment.
 9. The honeycomb filter according to claim6, wherein in the section of the honeycomb filter perpendicular to theaxial direction, the thickness of the partition wall is graduallyreduced toward the peripheral part from the central part with respect tosome or all of the partition walls of the honeycomb segment.
 10. Thehoneycomb filter according to claim 5, wherein the honeycomb filtercomprises a plurality of the honeycomb segments bonded by a bondingmaterial, and in the section of the honeycomb filter perpendicular tothe axial direction, the bonding material of the honeycomb segmentpositioned in a central part of the honeycomb filter is formed to bethicker than that of the honeycomb segment positioned in a peripheralpart.
 11. The honeycomb filter according to claim 5, wherein thehoneycomb filter comprises a plurality of the honeycomb segments bondedby a bonding material, and in the section of the honeycomb filterperpendicular to the axial direction, a thermal conductivity of thehoneycomb segment positioned in the central part of the honeycomb filteris higher than that of the honeycomb segment positioned in theperipheral part.
 12. The honeycomb filter according to claim 5, whereinthe plugging is performed in the honeycomb segment constituting thehoneycomb filter such that a plugging depth is large in the central partof the honeycomb segment, and small in the peripheral part, so that aheat capacity of the central part of the honeycomb filter is set to belarger than that of the peripheral part.
 13. The honeycomb filteraccording to claim 1, wherein a material of the filter contains oneselected from the group consisting of SiC, Si₃N₄, alumina, mullite,aluminum titanate, zirconium phosphate, and lithium aluminum silicate asa main crystal phase.
 14. The honeycomb filter according to claim 1,wherein a sectional shape of the through-hole is any of a triangle, atetragon, a hexagon and a corrugated shape.
 15. The honeycomb filteraccording to claim 5, wherein the honeycomb segment carries a catalyst.16. The honeycomb filter according to claim 15, wherein the catalystcontains at least one selected from the group consisting of Pt, Pd, Rh,K, Li, and Na.